Drugs used for anxiety making fish angry

Drugs used for anxiety in humans have been making freshwater fish more aggressive. But this is only the latest in a growing list of common drugs that are affecting our freshwater ecosystems.

Photo: Creative commons

An article in Science this week showed that a common anti-anxiety medication, which has been ending up in rivers from wastewater as patients on the medication pass it through their urine, is also affecting the mood of the European Perch (Perca fluviatilis), a species of freshwater water. Even tiny amounts of the drug has been found to make the timid fish more bold, anti-social and voracious, according to the recent study.

European Perch (Perca fluviatilis). Photo: Wikimedia commons

The drug in question is Oxazepam, part of the class of drugs known as benzodiazepines, which are the most commonly used anxiety drugs. It acts on neurons that suppress brain activity and relaxing the patients. But the drug seemed to have to opposite effect on Perch. It is thought that in the fish the drug acts to reduce the level of fear the fish experience. Michael Jonsson, co-author of the paper, explains that “if the fish were anxious to begin with, perhaps the drug reduces anxiety and allows the fish to become more active.” In the lab, that led to medicated fish from natural populations being more adventurous, tending to spend less time with their fellow fish, and eating more zooplankton.

Oxazepam is the latest in a growing list of drugs that are significantly altering fish behaviour and escaping into our waterways. A type of contraceptive pill, which contains the chemical 17-β-estradiol, and the widely used antidepressant Prozac (fluoxetine) have both been detected in rivers and have been shown to change to behaviour of the fathead minnow, a common freshwater fish species in the US. In another study it was discovered that Ibuprofen, one of the most commonly used anti-inflammatory drugs, caused a reduction in male zebrafishes’ libido.

This is a cause for concern because these drugs may have a negative impact upon freshwater ecosystems. For example, young perch eat zooplankton, which in turn feed on algae. If medicated perch have bigger appetites, that may potentially lead to algal blooms. However, Jonsson cautions that it is difficult to extrapolate from laboratory setting and make definitive claims about the effects in natural habitats.

Previously, it was thought that drug pollution in waterways was only of concern when the level of toxicity became lethal to freshwater species. But these studies are important because they highlight the significance of non-lethal effects of pollution from medication and how they may affect freshwater species and ecosystems.

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